This Pillowcase is very easy to make, you can decorate it any way you want or if you find a cute fabric pattern there is no need to go to that step but if you want to do the exact same as me here are the materials:

The fists step is to cut the fabric to fit the pillow, my pillow is a 30 cm square, so I cut a rectangle of 32 x 68 cm (added 2 cm for hem in the short side and extra fabric to allow overlap in the long side). Adjust your dimensions as needed for your pillow.